The present invention relates to novel phosphorus modified, porous magnesium silicates. More particularly the present invention relates to such phosphorus modified porous magnesium silicates having catalytic properties that are usefully employed in the alkylation of aromatic compounds.
Porous aluminosilicates, i.e., zeolites, especially highly siliceous forms thereof, such as ZSM-5, silicalite, ZSM-35, etc., are well-known in the art. Typically such compounds are porous crystalline frameworks based on an extended three-dimensional network of SiO.sub.4 and greater or lesser amounts of AlO.sub.4 tetrahedra linked to each other by shared oxygens. In U.S. Pat. No. 4,049,573 (Kaeding) it was disclosed that zeolites such as ZSM-5, ZSM-11, ZSM-12, ZSM-35, ZSM-38, etc., could be beneficially treated by impregnation with modifying substances including phosphorus compounds thereby preparing zeolitic catalysts having deposited or occluded modifying species. These modifiers are believed to affect the acid sites of the zeolites and were found to be useful catalysts in hydrocarbon conversion processes.
In U.S. Pat. No. 4,002,698, phosphorus modified aluminosilicates that are particularly suited for the alkylation of toluene were described. Preferred compounds possessed a silica/alumina ratio of at least about 12 and were modified by the addition thereto of at least 0.5 percent by weight phosphorus.
Numerous additional references teach that aluminosilicate zeolites may optionally further contain modifying substances including phosphorus. The phosphorus may be added by contacting the zeolite with an organic phosphorus compound or an inorganic phosphorus compound such as quaternary ammonium phosphate salts. Illustrative of such references are U.S. Pat. Nos. 4,140,726; 4,276,437; 4,276,438; 4,275,256; 4,278,827; 4,259,537; 4,230,894; 4,250,345; 3,962,364; 4,270,017, etc.
In 1972, U.S. Pat. No. 3,702,886 (Argauer) issued for a synthetic zeolite termed ZSM-5 and method for making same. This patent disclosed a zeolite having a SiO.sub.2 /Al.sub.2 O.sub.3 molar ratio from about 5 to 100. The main claim characterized ZSM-5 by reference to a table of X-ray diffraction lines (see Table I infra) and the following composition in terms of mole ratios of oxides EQU 0.9.+-.0.2 M.sub.2/n O:Al.sub.2 O.sub.3 :YSiO.sub.2 :ZH.sub.2 O
wherein M is at least one cation having a valance n, Y, is at least 5 and Z is between 0 and 40.
TABLE I ______________________________________ ZSM-5, Interplanar Spacing d(A) ______________________________________ 11.1 .+-. 0.2 6.30 .+-. 0.1 5.01 .+-. 0.1 3.71 .+-. 0.05 10.0 .+-. 0.2 6.04 .+-. 0.1 4.60 .+-. 0.08 3.04 .+-. 0.03 7.4 .+-. 0.15 5.97 .+-. 0.1 4.25 .+-. 0.08 2.99 .+-. 0.02 7.1 .+-. 0.15 5.56 .+-. 0.1 3.85 .+-. 0.07 2.94 .+-. 0.02 ______________________________________
According to Mobil scientists, the ZSM-5 aluminosilicate is prepared by including nitrogenous organic molecules such as tetrapropyl ammonium bromide in the reaction mixtures. For very high SiO.sub.2 /Al.sub.2 O.sub.3 preparations, no aluminum need be deliberately added since it is present as an impurity in the reactants. The organic molecules are incorporated into the framework structure as it forms and these as-synthesized materials are termed "nitrogenous zeolites". Application of high temperatures will free high SiO.sub.2 /Al.sub.2 O.sub.3 materials of these organic components without altering the basic framework structure, D. M. Olson et al., "Chemical and Physical Properties of the ZSM-5 Substitutional Series", J. Catal., 61, 390-396 at 391 (1980).